Intaglio plates and relief plates for printing, hologram original plates for relief holograms, microlens arrays and other various substrates with a concave-convex pattern formed thereon have been used in the art. For example, microlens arrays comprising microlenses arranged on a substrate have been used as means for efficiently focusing light from an illumination light source onto pixels in color liquid crystal displays (LCD) of a backlight system which have spread in recent years. Further, in color image sensors using CCD and the like, microlenses are arranged on the photoreceptive surface so as to correspond to photoreceptive cells in order to increase the effective numerical aperture. Also in optical fibers which have recently become increasingly used in optical communications and the like, microlenses are used in combination with optical fibers when optical coupling is contemplated.
In conventional methods for forming a concave-convex pattern, a concave-convex pattern is formed by providing a positive-working or negative-working photosensitive resin, exposing the photosensitive resin in a desired pattern, and developing the exposed resin, or by providing a positive-working or negative-working photosensitive resin, forming a mask in a predetermined pattern on a layer of the resin and etching the resin layer through the mask. These conventional methods suffer from problems of troublesome steps and low dimensional accuracy of concaves and convexes constituting the concave-convex pattern.
In recent years, color liquid crystal displays have drawn attention as flat displays. One example of the color liquid crystal displays is such that a color filter comprising a black matrix, a colored layer of a plurality of colors (in general, the three primary colors of red (R), green (G), and blue (B)), a transparent conductive layer (a common electrode), and an aligning layer is provided so as to face a thin film transistor (TFT element) array substrate, comprising a TFT transistor, an pixel electrode, and an aligning layer, while leaving a predetermined gap between the color filter and the TFT array substrate, and a liquid crystal material is poured into the gap to form a liquid crystal layer. In this type of color liquid crystal displays, the gap constitutes the thickness per se of the liquid crystal layer. Therefore, in order to realize good display properties, required of color liquid crystal displays, such as quick response, high contrast ratio, and wide angle of visibility, the thickness of the liquid crystal layer, that is, the distance between the color filter and the TFT array substrate, should be strictly held at a constant value.
A method for determining the thickness of the liquid crystal layer in color liquid crystal displays, which has been recently proposed in the art, is to pour a liquid crystal containing a large number of particles or rods, of glass, alumina, plastics or the like, called a spacer into gaps between the color filter and the TFT array substrate. In this case, the size of the spacer determines the size of the gap between two substrates, that is, the thickness of the liquid crystal layer.
In the above method for forming gaps between the color filter and the TFT array substrate, the following problems occur on the operation of color liquid displays. Specifically, gaps, which are even over the whole area of the color liquid crystal display, cannot be formed unless the density of the spacers dispersed on the surface of the substrate is proper with the spacers being evenly dispersed on the surface of the substrate. The deviation of the scattering in the thickness of gaps generally decreases with increasing the amount (density) of the spacer dispersed. Increasing the amount (density) of the spacers dispersed results in increased number of spacers present on display pixels, and, in the display pixels, the spacers constitute foreign materials in the liquid crystal material. The presence of spacers causes problems, such as disorder in alignment of liquid crystal molecules regulated by the aligning film and impossible regulation of alignment by ON/OFF of the voltage in the liquid crystal around the spacers. This poses a problem of a deterioration in display properties such as contrast ratio.
In order to overcome the above problems, a color filter provided with columnar convexes for determining the gaps (thickness of the liquid crystal layer) has been proposed (Japanese Patent Laid-Open No. 318816/1992 and the like). In this color filter, a colored layer is first formed, and a protective layer is then formed so as to cover the colored layer, followed by formation of columnar convexes using a photosensitive resin again by photolithography on the black matrix in its predetermined portions. This renders the process troublesome.
Further, more accurate regulation of substrate gaps than the regulation in TN liquid crystal modes is required, for example, in IPS (in-plane switching) liquid crystal modes which have recently drawn attractive attention. High coating accuracy of the photosensitive resin is required for regulation of the height of the columnar convexes so as to fall within .+-.0.3 .mu.m of the contemplated height which is necessary to cope with this demand. This raises problems associated with throughput, yield and the like.